Biomimetic Underwater Robots
Published on 24 Mar 2007 at 1:02 am.
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Filed under Fun, Research, Robotics.
Today we had a visit from Dr. Joseph Ayers of Northeastern University and the Marine Science Center. He spoke to us about his research in biomimetic underwater robots. Dr. Ayers is a marine biologist, a neuroscientist, and at this point an engineer, a roboticist, and a nonlinear dynamicist. He has been working on two types of robots: a lobster and a sea lamprey. The picture below is from their website and depicts their lobster robot that is now on display at the Smithsonian Cooper-Hewitt National Design Museum in New York City.
The lobster robot grew out of his research in trying to understand the neural circuitry of the lobster. Invertibrates, such as lobsters, are interesting to neurscientists because each individual of a given species has the same exact neurons. This means that one can actually identify and characterize individual neurons and the role that they play in the nervous systems of creatures like lobsters. By studying these circuits, Dr. Ayers has made significant progress in teasing apart the basic neural mechanisms behind animal locomotion.
They model the system with a Command System, a Coordinating System, a Central Pattern Generator, Proprioreceptive and Exteroreceptive Sensors, and Sensory Feedback (CCCPG for short). The Command System dictates the behavior generated by the Central Pattern Generator (CPG), such as: go forward, back up, defend, and flee. The Coordinating System determines the phase relationships between the muscles and limbs, which in turn controls the gait. Both of these systems modulate the Central Pattern Generator, which directly controls the muscles via the motor neurons. The Sensors and Sensory Feedback Systems are part of the peripheral system and serve to use incoming sensory information to modulate the behavior of the CPG. Sensory systems. By successfully reverse engineering the locomotive aspects of a lobster, one can demonstrate that one truly understands the system.
The sensors that the robot uses are all biomimetic. For example, antennae are used to sense water currents as well as detect potential collisions. Look closely at the picture and you will see that the antennae that they used were Strain Gauge Antenna, which one can buy for about $3.00.
The design of the muscles is fascinating…
Electric motors are too big and clunky, so the only remaining option is to use a material that can stretch and contract by themselves, and for that you need some sort of shape memory. They use Nitinol, which stands for NIckel TItanium Naval Ordnance Laboratory. Nitinol has two crystalinze states: martensite and austenite, and thermal changes can induce a phase transition between the two mineral states. Below a critical temperature, the Nitinol is martensite, which is a soft material, but when heated, a phase transition occurs and Nitinol transforms into the Austenite state, which is a high strength material. The Austenite state can be transformed to martensite by simply cooling the material. In the robot, they induce the phase change through heating by passing a 1 Amp current through the Nitinol wire. The ocean water then serves to cool the Austenite. The entire process serves to stretch and contract the wire muscle.
Dr. Ayers spent a sabbatical at the Institute for Nonlinear Science at the University of California at San Diego, where he learned the necessary nonlinear dynamics to introduce chaos into the neural circuitry. He hypothesized that the animal uses chaotic behavior to get its muscles to wiggle it out of tight spots. This strategy indeed works, and is quite impressive.
In addition to having their early robots on display at the Smithsonian, Dr. Ayers is getting a impressive amount of publicity. He has been featured in Science, Wired News, and will be in next months Men’s Vogue. That is an accomplishment that most scientists will never achieve!
I learned some other interesting facts from Dr. Ayers. One was that the center of buoyancy on a fish is below its center of mass. This is why dead fish go belly up! I can’t help but wonder why this should be the case? Fighter jets are actually designed to be right at the edge of instability. A stable aircraft is not very manueverable. Is it possible that this unstable configuration in the living fish keeps the fish near the edge of stability so that is somehow is also at the edge of stability and thus maximally manueverable? I really don’t know.
He also explained that terrestrial animals expend 95% of their locomotive energy to support themselves against gravity, and 5% of their locomotive energy towards translational motion. On the other hand, aquatic animals expend 95% of their locomotive energy toward translational motion, and 5% fighting hydrodynamic resistance.
Kevin Knuth
Albany NY
